Abstract: The invention relates to the design of the profiles of two meshing rotors, which are provided with helical lands and intervening grooves and adapted for rotation around parallel axes in a working space in a rotary screw machine, where one groove in one rotor (female rotor 1) co-operates with a corresponding land on a second rotor (male rotor 2), so that a chevron shaped chamber is formed by the flanks of the groove and the land, with the open legs of the chamber ending at the high-pressure end of the machine. The flank profiles according to the invention are designed so that the torque acting on the female rotor by the gas forces in the machine is 17-19.5%, preferably about 18.5%, of the corresponding torque on the male rotor, and that the blow hole area formed hereby at the high-pressure side of the rotor mesh does not exceed a value corresponding to 25 mm.sup.